Terminals or smartphones on board aircraft, ships, trains, trucks, cars, or carried by pedestrians need to be connected while on the move. These devices need short and very long range communication capabilities for voice and data at a high-throughput and a low power budget, including to watch or listen to multimedia content (video or audio), or participate in interactive games. All kinds of objects on-board vehicles or located in a manufacturing plant, an office, a warehouse, a storage facility, retail establishments, hospitals, sporting venues, or a home are connected to the Internet of Things (IoT): tags to locate and identify objects in an inventory or to keep people in or out of a restricted area; devices to monitor physical activity or health parameters of their users; sensors to capture environmental parameters (concentration of pollutants; hygrometry; wind speed, etc.); actuators to remotely control and command all kinds of appliances, or more generally, any type of electronic device that could be part of a command, control, communication and intelligence system, the system being for instance programmed to capture/process signals/data, transmit the same to another electronic device, or a server, process the data using processing logic implementing artificial intelligence or knowledge based reasoning and return information or activate commands to be implemented by actuators.
RF communications are more versatile than fixed-line communications for connecting these types of objects or platforms. As a consequence, radiofrequency T/R modules are and will be more and more pervasive in professional and consumer applications. A plurality of T/R modules may be implemented on the same device. By way of example, a smartphone typically includes a cellular communications T/R module, a Wi-Fi/Bluetooth T/R module, a receiver of satellite positioning signals (from a Global Navigation Satellite System or GNSS). WiFi, Bluetooth and 3 or 4G cellular communications are in the 2.5 GHz frequency band (S-band). GNSS receivers typically operate in the 1.5 GHz frequency band (L-band). RadioFrequency IDentification (RFID) tags operate in the 900 MHz frequency band (UHF) or lower. Near Field Communication (NFC) tags operate in the 13 MHz frequency band (HF) at a very short distance (about 10 cm).
It seems that a good compromise for IoT connections lies in VHF or UHF bands (30 to 300 MHz and 300 MHz to 3 GHz) to get sufficient available bandwidth and range, a good resilience to multipath reflections as well as a low-power budget.
A problem to be solved for the design of T/R modules at these frequency bands is to have antennas which are compact enough to fit in the form factor of a connected object. A traditional omnidirectional antenna of a monopole type, adapted for VHF bands, has a length between 25 cm and 2.5 m (λ/4). A solution to this problem is notably provided by PCT application published under n° WO2015007746, which has the same inventor and is co-assigned to the applicant of this application. This application discloses an antenna arrangement of a bung type, where a plurality of antenna elements are combined so that the ratio between the largest dimension of the arrangement and the wavelength may be much lower than a tenth of a wavelength, even lower than a twentieth or, in some embodiments than a fiftieth of a wavelength. To achieve such a result, the antenna element which controls the fundamental mode of the antenna is wound up in a 3D form factor, such as, for example, a helicoid so that its outside dimensions are reduced relative to its length.
But there is also a need for the connected devices to be compatible with terminals which communicate using WiFi or Bluetooth frequency bands and protocols. In this use case, some stages of the T/R module have to be compatible with both VHF and S bands. If a GNSS receiver is added, a T/R capacity in L band is also needed. This means that the antenna arrangements of such devices should be able to communicate simultaneously or successively in different frequency bands. Adding as many antennas as frequency bands is costly in terms of form factor, power budget and materials. This creates another challenging problem for the design of the antenna. Some solutions are disclosed for base station antennas by PCT applications published under n° WO200122528 and WO200334544. But these solutions do not operate in VHF bands and do not provide arrangements which would be compact enough in these bands.
The applicant of this application has filed a European patent application under n° EP2016/306059.3 that has the same inventor as this application. This application discloses an antenna arrangement comprising: a first conductive element configured to radiate above a defined frequency of electromagnetic radiation; one or more additional conductive elements located at or near one or more positions defined as a function of positions of nodes of current (i.e. zero current or Open Circuit positions) of harmonics of the electromagnetic radiation.
This earlier application does not disclose how to adjust the frequency bandwidths around the defined frequency of electromagnetic radiation or its harmonics. It would be desirable to control these frequency bandwidths so as to be able to ensure a defined throughput, or to meet the performance requirements of various standards for radiocommunication such as IEEE 802.11, 802.15.4 etc., for instance for transmitting multimedia contents with a defined quality of service. The instant invention discloses a solution to this problem.